The impedance of a component is the resistance of that component for AC voltages. The symbol for resistance is R; the symbol for impedance is X. The impedance of an inductor is not zero; it depends on the inductance (number of turns; core material) and the frequency of the signal (number of polarity changes (forth and back) per second). The impedance can be calculated using the following equation.

f is the frequency in Hertz; L is the inductance in Henry

Example: We have a 1mH inductor and connect it to a 50Hz AC voltage source. Calculate the impedance of the inductor.

X_L = 2∙π∙50∙10^-3 = 0.31Ω.